Changes in epidermal radiosensitivity with time associated with increased colony numbers

Epidermal clonogenic cell survival and colony formation following irradiation were investigated and related to radiosensitivity. A rapid in vivo/in vitro assay was developed for the quantification of colonies arising from surviving clonogenic cells in pig epidermis after irradiation. Bromodeoxyuridine (BrdU)-labelled cells in full thickness epidermal sheets were visualized using standard immunohistochemistry. In unirradiated skin, approximately 900 BrdU-positive cells mm(-2) were counted. In a time sequence experiment, BrdU-positive cell numbers increased from an average of 900 cells mm(-2) to approximately 1400 cells mm(-2) after BrdU-labelling for 2-24 h. In irradiated skin, colonies containing >/=16 BrdU-positive cells were seen for the first time at days 14/15 after irradiation. The number of these colonies per cm(2) as a function of skin surface dose yielded a cell survival curve with a D(0)-value (+/-SE) of 3.9+/-0.6 Gy. This relatively high D(0)-value is possibly due to a rapid fall off in depth dose distribution for the iridium-192 source and consequently a substantial contribution of hair follicular epithelium to colony formation. At 14/15 days after irradiation, the ED(50) level of 33.6 Gy for the in vivo response of moist desquamation corresponded with 2.7 colonies cm(-2). Surprisingly, the number of colonies increased with time after irradiation with an estimated doubling time of approximately 4 days, while the D(0)-value remained virtually unchanged. This increase in colony numbers could be due to migration of clonogenic cells, to the recruitment of dormant clonogenic cell survivors by elevated levels of cytokines, or to both. Although frequent biopsying caused increased cytokine levels, which had a systemic effect on unirradiated skin, it had no influence on colony formation in irradiated skin. Smaller colonies, containing 4-8 cells or 9-15 cells, were abundant, particularly after higher doses, which resulted in higher D(0)-values. The majority of these small colonies were abortive and did not progress to larger colonies. There was no statistical evidence for significant variations in the interanimal responses.     

Correlation of the dose-response relationships for epidermal colony-forming units, skin reactions, and healing, in the X-irradiated mouse tail

The sensitivity of epidermal colony-forming units (CFU) in the mouse tail has been compared with the sensitivity of target units responsible for healing the epidermis (EHU). The value of D0 for epidermal CFU was 3.45 +/- 0.36 Gy, much higher than most earlier reports for CFU in dorsal epidermis. The reason for the high D0 is unknown, but it is considered unlikely to be due to marked hypoxia. The value of D0 for EHU was 2.78 +/- 0.51 Gy, which was deduced from the steepness of the dose-incidence curve for the healing of tails. A comparison of the two values of D0 indicates that the inactivation rate of CFU can account for the steepness of the dose-response curve for survival of the tissue. The dose which allowed 50% of tails to heal well corresponded to 3-4 colonies per cm2 of epidermis, to a median peak skin reaction of about 2 (moist desquamation) on an arbitrary scoring scale, and to a slightly lower median skin reaction of 1.7 when the reaction scores were averaged over the period 3 to 6 weeks after irradiation.     

Manipulation of the radiosensitivity of pig epidermis by changing the concentration of oxygen and halothane in the anaesthetic gas mixture

A gas mixture of halothane, oxygen and nitrous oxide has been used to anesthetize pigs for irradiation. The effects of various concentrations of halothane and oxygen on the radiosensitivity of the epidermis were examined after irradiation with single doses of beta-rays from strontium-90 plaques. The incidence of moist desquamation was used as an endpoint, and experiments were compared on the basis of the dose associated with a 50 per cent incidence of moist desquamation (ED50 +/- SE). For pigs inspiring an anaesthetic gas mixture of 2 per cent halothane, approximately 70 per cent oxygen and approximately 30 per cent nitrous oxide the ED50 for moist desquamation was 27.32 +/- 0.52 Gy. A similar ED50 value of 27.39 +/- 1.20 Gy was obtained when 4 per cent halothane was used in place of 2 per cent. When the pigs were breathing air (approximately 21 per cent oxygen) in place of oxygen and nitrous oxide the ED50 values were increased significantly to 31.25 +/- 0.94 Gy and 33.72 +/- 1.08 Gy for 2, and 4 per cent halothane, respectively. This change in the radiosensitivity of the epidermis was represented by dose modification factors of approximately 1.13 and approximately 1.23 for 2 and 4 per cent halothane, respectively. Irradiation with a high oxygen concentration in the inspired gas mixture did not result in any significant variation of the dose required to produce moist desquamation in 50 per cent of the fields irradiated for dorsal, lateral and ventral positioned skin fields on the flank. However, pigs breathing air and halothane during irradiation showed marked differences in the radiosensitivity of the various sites on the flank, with ED50 values for moist desquamation of approximately 37 Gy and 26-30 Gy for dorsal and ventral positioned fields, respectively. This marked difference in radiosensitivity suggests variations in the physiological compensation over the flank when pigs are breathing oxygen at low concentrations under anaesthesia.     

Evidence for humoral effects on the radiation response of rat foot skin.

The influence of perturbation of the physiologic state of the whole body on the outcome of radiation exposure has been examined in a rat foot model. Irradiation was carried out using 60Co gamma-rays. Moist desquamation was used as an endpoint. Rats were given a priming dose of 2 Gy, 4 Gy or 7 Gy to their whole body except their hind feet (partial body priming dose). After a variable time period both hind feet of these animals were irradiated with graded doses of 60Co gamma-rays. The incidence of moist desquamation in the irradiated feet of these animals was compared with the incidence of moist desquamation in animals that had not received the initial partial body priming dose. It was noticed that the incidence of moist desquamation in the rat foot skin of animals that received 7 Gy partial body priming dose 4 h prior to irradiation of their hind feet was significantly less than moist desquamation in control animals. The ED(50) value of 22.53+/-0.16 Gy for moist desquamation of the foot skin of control animals was significantly lower (p<0.01) than the value of 25.25+/-0.29 Gy obtained for animals that received a partial body priming dose of 7 Gy 4 h prior to irradiation of their hind feet. It was concluded that the response of rat foot skin to radiation was not purely the result of epidermal stem cell kill and that it can be modified by alterations in the overall physiological state of the animal's body brought about by a priming dose to the whole of the animal's body except the hind feet.     

Changes in the cell kinetics of pig epidermis after single doses of X rays

Changes in the cell kinetics of pig epidermis have been investigated after irradiation with single doses of 15 Gy and 20 Gy of X rays. The epidermis exhibited an initial degenerative phase when the rate of cell depletion was independent of radiation dose. Changes consistent with repopulation were evident between the 14th and 18th day after irradiation. The severity of cell depletion and the rate of recovery of the epidermis were dose dependent. The regenerative phase was characterized by an increased cell proliferation; values for the labelling index (LI) were greater than those in the non-irradiated epidermis, from 14 days after 15 Gy and from 18 days after 20 Gy. The LI was still elevated at the end of the observation period, i.e. Day 56. No change in the time for DNA synthesis was found. Eighteen days after 15 Gy and 22 days after 20 Gy, islands of cells (colonies), with an appearance similar to the cells in the normal epidermis, were seen. The minimum turnover time (TT) for the proliferating cells of the basal layer of the epidermis in radiation-damaged skin was 61-68 h as compared with 125 h in unirradiated skin. For the basal cells in the colonies, TT was 16-22 h.     

The effect of Captopril on benign and malignant reactions in irradiated rat skin

The effect of the angiotensin converting enzyme inhibitor Captopril on the severity of radiation-induced epilation and moist desquamation and the incidence of skin tumours was determined for up to 52 weeks in male rats. The irradiation consisted of a range of single doses (0, 10, 20, 30 Gy) of 60Co gamma rays to a 3.5 cm2 right hemithorax port. Half of each radiation dose group consumed control powdered chow, and half consumed chow containing Captopril (50 mg/kg/day) continuously after irradiation. There were time- and radiation-dose-dependent increases in all three skin reactions. Rats exposed to 10 Gy exhibited a mild and transient epilation, but no moist desquamation or neoplasia in the radiation port. In animals exposed to 30 Gy, however, epilation began at 2 weeks after irradiation, reached a peak at approximately 7 weeks, then persisted essentially unchanged through 52 weeks. Captopril had no significant effect on the epilation reaction. Two waves of moist desquamation were observed after 30 Gy. The first appeared at 3 weeks after irradiation, reached a peak from 6-10 weeks, then subsided partially but significantly from 12-26 weeks. The second wave of moist desquamation began at 26-28 weeks, often was ulcerative, and occasionally was accompanied by the appearance of tumours in the irradiated volume. Captopril significantly (p less than 0.05) reduced the severity of both phases of the moist desquamation reaction after 30 Gy, and reduced the percentage of animals exhibiting the most severe desquamation score (involving 50% of the radiation port). Of particular interest was the observation that Captopril also reduced the incidence of tumours. Of the 14 tumours detected, all were malignant (fibrosarcomas, squamous cell carcinomas), and only three (p less than 0.05) occurred in rats receiving Captopril. Multiple tumours (three cases), tumours induced by 20 Gy (three cases), and tumours appearing before 6 months (one case) were observed only in rats consuming control diet, never in Captopril-treated animals. Animals which developed tumours in the second 6 months post-irradiation exhibited significantly more severe moist desquamation during the first 6 months than did the tumour-free members of their treatment group. Thus Captopril, known to ameliorate acute lung damage in irradiated rats, also reduces chronic benign and malignant skin reactions in the radiation treatment field.     

Single dose irradiation response of pig skin: a comparison of brachytherapy using a single, high dose rate iridium-192 stepping source with 200 kV X-rays

An experimental brachytherapy model has been developed to study acute and late normal tissue reactions as a tool to examine the effects of clinically relevant multifractionation schedules. Pig skin was used as a model since its morphology, structure, cell kinetics and radiation-induced responses are similar to human skin. Brachytherapy was performed using a microSelectron high dose rate (HDR) afterloading machine with a single stepping source and a custom-made template. In this study the acute epidermal reactions of erythema and moist desquamation and the late dermal reactions of dusky mauve erythema and necrosis were evaluated after single doses of irradiation over a follow-up period of 16 weeks. The major aims of this work were: (a) to compare the effects of iridium-192 (192Ir) irradiation with effects after X-irradiation; (b) to compare the skin reactions in Yorkshire and Large White pigs; and (c) to standardize the methodology. For 192Ir irradiation with 100% isodose at the skin surface, the 95% isodose was estimated at the basal membrane, while the 80% isodose covered the dermal fat layers. After HDR 192Ir irradiation of Yorkshire pig skin the ED50 values (95% isodose) for moderate/severe erythema and moist desquamation were 24.8 Gy and 31.9 Gy, respectively. The associated mean latent period (+/- SD) was 39 +/- 7 days for both skin reactions. Late skin responses of dusky mauve erythema and dermal necrosis were characterized by ED50 values (80% isodose) of 16.3 Gy and 19.5 Gy, with latent periods of 58 +/- 7 days and 76 +/- 12 days, respectively. After X-irradiation, the incidence of the various skin reactions and their latent periods were similar. Acute and late reactions were well separated in time. The occurrence of skin reactions and the incidence of effects were comparable in Yorkshire and Large White pigs for both X-irradiation and HDR 192Ir brachytherapy. This pig skin model is feasible for future studies on clinically relevant multifractionation schedules in a brachytherapy setting.     

Protection of pig epidermis against radiation-induced damage by the infusion of BW12C.

BW12C, which was developed as an agent for the treatment of sickle cell anaemia, increases the binding of oxygen to haemoglobin and hence reduces the availability of oxygen to tissues. Due to these changes in oxygen availability BW12C could act as a protector against radiation-induced injury to normal tissues. In this study the potential value of BW12C, as a radioprotector, was studied in the irradiated epidermis of the pig. The infusion of BW12C caused an instant left shift of the oxygen dissociation curve, an effect that lasted for approximately 1.5 h. This left shift in the oxygen dissociation curves increased with increasing dose of the drug. There appeared to be no long-term systemic effects produced by doses of 20-100 mg/kg of BW12C. In the first 90 min after the infusion of BW12C skin fields were irradiated with single doses of beta-rays from strontium-90 plaques. The incidence of moist desquamation was used as an endpoint for assessing the severity of the radiation response. With animals breathing approximately 70% oxygen in the anaesthetic gas mixture, the ED50 values for moist desquamation were 30-31 Gy after a dose of 30 and 50 mg/kg, and 37-38 Gy for 75 and 100 mg/kg doses of BW12C. These ED50 values were significantly higher than the value of 27.3 Gy for radiation alone. This indicated dose modification factors (DMF) with mean values of approximately 1.13 and approximately 1.40 for irradiation following the infusion of low (30-50 mg/kg) and high (75-100 mg/kg) doses of the drug, respectively. With the animals breathing air (approximately 21% of oxygen) in the 2% halothane anaesthesia gas mixture, irradiation in the presence of 30 and 50 mg/kg of BW12C resulted in ED50 values of approximately 39 Gy for moist desquamation, which was significantly higher than the value of 31.2 Gy for radiation alone. Surprisingly, a higher dose of 75 mg/kg of BW12C resulted in a lower ED50 value for moist desquamation of 34.38 Gy. Irradiation in the presence of a dose of 100 mg/kg of BW12C produced an ED50 value which was not significantly different from that for radiation alone. In the situation where animals were breathing air (approximately 21% oxygen) during irradiation a DMF of 1.14 was obtained for irradiation alone, when the results were compared with those for irradiation alone with approximately 70% oxygen in the anaesthetic gas mixture.(ABSTRACT TRUNCATED AT 400 WORDS)     

X-ray irradiation of the human epidermis in vitro. II. Comparison of a single 44 kV and 200 kV x-ray irradiation

On example of the reduction of epidermal binding of FITC-wheat germ agglutinin (WGA) the direct membrane effect of a single roentgen irradiation (44 kV and 220 kV) was analysed in vitro. Human normal skin and psoriasis centre were compared. Normal skin showed no alteration of light-microscopically visible FITC-WGA-binding on epidermal cells over the whole doses range. Psoriatic lesions responded to doses of greater than or equal to 5 Gy (44 and 220 kV) with a drastic reduction of epidermal lectin adhesion to lower and middle cell layers. The maximum of efficacy was with 5 Gy (44 kV) or 10 Gy (220 kV). A dose elevation up to 20 Gy did not result in an increase of efficacy. Topographically the radiosensitive FITC-WGA-binding could be seen in the rete ridges above all. The findings support the impression of an increased radiosensitivity of the lesional psoriasis epidermis compared with normal skin. The causes for this are seen in an abnormal differentiation of keratinocytes in psoriasis.     

Protection of Pig Epidermis against Radiation-induced Damage by the Infusion of BW12C

Summary

BW12C, which was developed as an agent for the treatment of sickle cell anaemia, increases the binding of oxygen to haemoglobin and hence reduces the availability of oxygen to tissues. Due to these changes in oxygen availability BW12C could act as a protector against radiation-induced injury to normal tissues. In this study the potential value of BW12C, as a radioprotector, was studied in the irradiated epidermis of the pig. The infusion of BW12C caused an instant left shift of the oxygen dissociation curve, an effect that lasted for ～1·5 h. This left shift in the oxygen dissociation curves increased with increasing dose of the drug. There appeared to be no long-term systemic effects produced by doses of 20–100 mg/kg of BW12C. In the first 90 min after the infusion of BW12C skin fields were irradiated with single doses of β-rays from strontium-90 plaques. The incidence of moist desquamation was used as an endpoint for assessing the severity of the radiation response. With animals breathing ～70% oxygen in the anaesthetic gas mixture, the ED₅₀ values for moist desquamation were 30–31 Gy after a dose of 30 and 50 mg/kg, and 37–38 Gy for 75 and 100 mg/kg doses of BW12C. These ED₅₀ values were significantly higher than the value of 27·3 Gy for radiation alone. This indicated dose modification factors (DMF) with mean values of ～1·13 and ～1·40 for irradiation following the infusion of low (30–50 mg/kg) and high (75–100 mg/kg) doses of the drug, respectively. With the animals breathing air (～21% of oxygen) in the 2% halothane anaesthesia gas mixture, irradiation in the presence of 30 and 50 mg/kg of BW12C resulted in ED₅₀ values of ～39 Gy for moist desquamation, which was significantly higher than the value of 31·2 Gy for radiation alone. Surprisingly, a higher dose of 75 mg/kg of BW12C resulted in a lower ED₅₀ value for moist desquamation of 34·38 Gy. Irradiation in the presence of a dose of 100 mg/kg of BW12C produced an ED₅₀ value which was not significantly different from that for radiation alone. In the situation where animals were breathing air (～21% oxygen) during irradiation a DMF of 1·14 was obtained for irradiation alone, when the results were compared with those for irradiation alone with ～70% oxygen in the anaesthetic gas mixture. When this ‘air component’ is taken into account DMF values of ～1·3 were obtained for 30 and 50 mg/kg of BW12C, whereas for 75 and 100 mg/kg of BW12C this was reduced to 1·11 and 1·0, respectively. These modifications in the sensitivity of the epidermis for irradiation in the presence of various doses of BW12C were not uniform over the flank skin of the pig. For all doses of BW12C used, the skin fields positioned dorsally on the flank always showed a reduced radiosensitivy when compared with the ventrally positioned skin sites. This suggested a better physiological compensation for the effect produced by the drug in the ventral area of the flank skin. A similar variation in the radiosensitivity over the flank was noted for radiation alone when pigs were breathing air (～21% oxygen) in the anaesthetic gas mixture. Only when animals were breathing ～70% oxygen in the anaesthetic gas mixture was the radiosensitivity of the skin uniform over the whole flank.     

鼻咽癌放疗后继发性皮肤晚期放射损伤

目的 通过分析皮肤早期放射反应对皮肤晚期放射反应的影响,探讨皮肤的继发性晚期放射损伤。方法 对门诊随访的放疗后生存5年以上的335例鼻咽癌患者进行调查研究,其中放疗时中位年龄41岁(12～67岁),240例伴颈部淋巴结转移。鼻咽原发灶首程放疗中位剂量为70Gy(55～86Gy),以面颈野为主野放疗71例,以耳前野为主野放疗264例。颈部根治性放疗中位剂量为64Gy(46～72Gy),预防照射中位剂量为55Gy(21～67Gy)。48例合并化疗。根据1995年SOMA标准评价皮肤晚期放射反应。结果 随访间隔中位时间为14年(5～38年)。63例无皮肤晚期反应,1、2、3、4级皮肤晚期反应发生率分别为43.9%(147例)、20.9%(70例)、13.7%(46例)、2.7%(9例)。44例放疗中出现湿性脱皮反应,其中1、2、3、4级皮肤晚期反应发生率分别为41%(18例)、23%(10例)、30%(13例)和5%(2例);无湿性脱皮患者的相应发生率分别为44.3%(129例)、20.6%(60例)、11.3%(33例)和2.4%(7例),两者差异有统计学意义(χ²=17.42,P=0.002)。分层分析结果显示初诊时是否伴颈部淋巴结转移、放疗野及颈部淋巴结放疗剂量均对皮肤晚期反应发生有关,而性别、年龄及是否联合使用化疗与皮肤晚期反应的发生无关。 结论 严重的皮肤早期放射反应可能增加皮肤晚期放射反应,可能存在继发性皮肤晚期放射损伤。     

Cell kinetic changes in the follicular epithelium of pig skin after irradiation with single and fractionated doses of X rays

Changes in the cell kinetics of the follicular epithelium of the pig have been studied after irradiation with single and fractionated doses (30 fractions/39 days) of X rays and the results compared with previously published data for the epidermis. In the follicular epithelium there was an initial degenerative phase, during which the rate of cell depletion was independent of the radiation dose and the mode of administration. Evidence for repopulation was seen between the 14th and 18th days after single doses (15 or 20 Gy) and by the 28th day after the start of irradiation with fractionated doses (52.3-80.0 Gy). However, the degree of cell depletion and the subsequent rate of repopulation were independent of dose. The regenerative phase was characterized by an increased cell proliferation as indicated by an elevation of the labelling index. Islands of cells (colonies), with an appearance similar to cells in the normal follicular epithelium, were seen 18 days after a single dose of 20 Gy and 42 days after the start of fractionated irradiation. When compared with the epidermis, the follicular epithelium exhibited considerably less evidence of damage after both single and fractionated doses of X rays. There was a lower incidence of degenerate cells and reduced levels of cell depletion in the follicular epithelium, suggesting that cells from this region play an important role in the repopulation of the epidermis after high-dose irradiation.     

The skin: its structure and response to ionizing radiation

The response of the skin to ionizing radiation has important implications both for the treatment of malignant disease by radiation and for radiological protection. The structural organization of human skin is described and compared with that of the pig, with which it shows many similarities, in order that the response of the skin to ionizing radiation may be more fully understood. Acute radiation damage to the skin is primarily a consequence of changes in the epidermis; the timing of the peak of the reaction is related to the kinetic organization of this layer. The rate of development of damage is independent of the radiation dose, since this is related to the natural rate of loss of cells from the basal layer of the epidermis. Recovery of the epidermis occurs as a result of the proliferation of surviving clonogenic basal cells from within the irradiated area. The presence of clonogenic cells in the canal of the hair follicle is important, particularly after non-uniform irradiation from intermediate energy beta-emitters. The migration of viable cells from the edges of the irradiated site is also significant when small areas of skin are irradiated. Late damage to the skin is primarily a function of radiation effects on the vasculature; this produces a wave of dermal atrophy after 16-26 weeks. Dermal necrosis develops at this time after high doses. A second phase of dermal thinning is seen to develop after greater than 52 weeks, and this later phase of damage is associated with the appearance of telangiectasia. Highly localized irradiation of the skin, either to a specific layer (as may result from exposure to very low energy beta-emitters) or after exposure to small highly radioactive particles, 'hot particles', produces gross effects that become visibly manifest within 2 weeks of exposure. These changes result from the direct killing of the cells of the skin in interphase after doses greater than 100 Gy. Dose-effect curves have been established for the majority of these deterministic endpoints in the skin from the results of both experimental and clinical studies. These are of value in the establishment of safe radiation dose limits for the skin.     

The Skin: Its Structure and Response to Ionizing Radiation

Summary

The response of the skin to ionizing radiation has important implications both for the treatment of malignant disease by radiation and for radiological protection. The structural organization of human skin is described and compared with that of the pig, with which it shows many similarities, in order that the response of the skin to ionizing radiation may be more fully understood. Acute radiation damage to the skin is primarily a consequence of changes in the epidermis; the timing of the peak of the reaction is related to the kinetic organization of this layer. The rate of development of damage is independent of the radiation dose, since this is related to the natural rate of loss of cells from the basal layer of the epidermis. Recovery of the epidermis occurs as a result of the proliferation of surviving clonogenic basal cells from within the irradiated area. The presence of clonogenic cells in the canal of the hair follicle is important, particularly after non-uniform irradiation from intermediate energy β-emitters. The migration of viable cells from the edges of the irradiated site is also significant when small areas of skin are irradiated. Late damage to the skin is primarily a function of radiation effects on the vasculature; this produces a wave of dermal atrophy after 16–26 weeks. Dermal necrosis develops at this time after high doses. A second phase of dermal thinning is seen to develop after > 52 weeks, and this later phase of damage is associated with the appearance of telangiectasia. Highly localized irradiation of the skin, either to a specific layer (as may result from exposure to very low energy β-emitters) or after exposure to small highly radioactive particles, ‘hot particles’, produces gross effects that become visibly manifest within 2 weeks of exposure. These changes result from the direct killing of the cells of the skin in interphase after doses > 100 Gy. Dose-effect curves have been established for the majority of these deterministic endpoints in the skin from the results of both experimental and clinical studies. These are of value in the establishment of safe radiation dose limits for the skin.     

Cell population kinetics of the rhabdomyosarcoma R1H of the rat after single doses of X-rays

The kinetics of depopulation and repopulation of the solid transplantable rhabdomyosarcoma R1H of the rat following local irradiation with single subcurative X-ray doses of 7.5, 15 and 30 Gy was studied. Several parameters were sequentially measured over a time interval of 4 weeks after irradiation: the ratio of the number of tumour to host cells, and the cellular DNA content of tumour and host cells, were determined by flow cytometry; the amount of DNA per gram of tumour tissue was determined biochemically; the clonogenic fraction of tumour cells was obtained from in vitro colony assay; and the tumour volume was assessed by in situ caliper measurements. From the amount of DNA per gram and the average DNA content per cell, the total number of cells per gram of tumour tissue was obtained. From this and the other parameters measured, the number of clonogenic tumour cells, non-clonogenic tumour cells and nucleated host cells per tumour, as well as their variation with time and dose, could be derived. The results showed that there was a lag period prior to depopulation amounting to 3.8 +/- 1.4, 1.4 +/- 0.8 or 0 +/- 0.7 days for 7.5, 15 or 30 Gy, respectively. The rate of depopulation of non-clonogenic tumour cells increased with dose; the halving times of non-clonogens were 4.7 +/- 1.8, 2.6 +/- 0.7 or 2.1 +/- 0.4 days for the three doses applied. There were no indications that proliferation of doomed cells contributed significantly to tumour growth after irradiation. After lag periods that were similar in length to those prior to depopulation, a massive immigration of host cells was observed. Under certain conditions more than 97 per cent of the cells present in irradiated tumours were found to be of host origin. There was a lag period before the onset of repopulation by clonogenic tumour cells, the length of which increased from 2.7 +/- 0.7 to 5.0 +/- 0.8 or 6.3 +/- 1.0 days for 7.5, 15 or 30 Gy, respectively. The initial rate of repopulation increased with radiation dose; after the end of the lag period the doubling time of clonogenic tumour cells (in controls amounting to 3.7 +/- 0.2 days) was 3.1 +/- 0.1, 2.1 +/- 0.1 and 1.1 +/- 0.1 days for the three doses applied.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effects of Lipochromin and Levosinum in the modulation of radiation-induced injury to pig skin

Pig skin was used as a model to study the effectiveness of two topically applied creams, Lipochromin and Levosinum, in modifying the development of both early and late radiation damage to pig skin. Irradiated skin sites that received daily topical application of Levosinum or Lipochromin after exposure were compared with sites on the contralateral flank of the same animal that received irradiation only. Irradiation was with graded doses of 90Sr/90Y beta-rays. Incidence of moist desquamation (acute) and ischaemic dermal necrosis (late) were used as end-points. The latency period for the development of moist desquamation and its healing time was also assessed. The latency period for the development of moist desquamation in this model ranged from 4.00-6.75 weeks. There was no significant difference between the cream treatment and control sites. Application of Levosinum shortened the healing time of moist desquamation at each dose level by 5-10 days. In three out of four dose levels used, this shortening of the healing time was statistically significant (p < 0.03). Treatment with these topical applications also reduced the incidence of late dermal necrosis and increased the ED50 values for the incidence of dermal necrosis. This increase in ED50 values was equivalent to a dose modification factor of 1.11-1.13.     

The relative biological effectiveness of fractionated doses of fast neutrons (42 MeVd----Be) for normal tissues in the pig. I. Effects on the epidermis and dermal vascular/connective tissues

The effects of fractionated doses of fast neutrons (42 MeVd----Be) on the early epithelial and later dermal response of pig skin have been assessed and compared with those after X irradiation. For the early epithelial reaction, i.e. moist desquamation, the relative biological effectiveness (RBE) of the neutron beam increased with the decreasing size of the X-ray dose/fraction. There was an experimentally observed upper RBE value of approximately 2.75 for X-ray doses/fraction of between 2 and 5 Gy. For the late reaction of ischaemic dermal necrosis the RBE was greater than 3.0 for X-ray doses/fraction of less than 3 Gy and, based on the assumptions made in the linearquadratic model of cell survival, an upper limiting RBE of 4.32 +/- 0.39 was calculated for infinitely small doses/fraction. These findings were compared with other radiobiological data and the conclusions drawn from the results of clinical trials. It was concluded that for the sparing of late effects in skin and subcutaneous tissues, relative to acute reactions, a relatively small number of fractions in a short overall treatment time may be optimal for fast neutron therapy.     

He-Ne激光照射对豚鼠表皮Langerhans细胞的影响

目的 观察不同剂量Ｈｅ－Ｎｅ激光照射对Ｌａｎｇｅｒｈａｎｓ细胞产生的影响。方法 ５６只Ｄｕｎｋｉｎ－Ｈａｒｔｌｅｙ雄性白色豚鼠分７组,每组８只。６组为激光照射组,分别给予１．１６、２．３２、４．６５Ｊ／ｃｍ＾２的Ｈｅ－Ｎｅ激光照射（各２组）,每日１次;另１组为对照组。连续照射７天后,第１、３天麻醉下活体取豚鼠照射区皮肤,采用ＡＴＰ酶染色法测定ＡＴＰ酶阳性细胞（Ｌａｎｇｅｒｈａｎｓ细胞）密度。结果 ２．３２Ｊ／ｃｍ＾２的Ｈｅ－Ｎｅ激光照射后第１、３天组和４．６５Ｊ／ｃｍ＾２的Ｈｅ－Ｎｅ激光照射后第１天组的豚鼠,其表皮ＡＴＰ酶阳性细胞密度均高于对照组,差异均有非常显著意义（Ｐ〈０．０１）。结论 一定剂量的Ｈｅ－Ｎｅ激光照射可增加豚鼠表皮Ｌａｎｇｅｒｈａｎｓ细胞的数量,其数量的增加可能影响Ｌａｎｇｅｒｈａｎｓ细胞的抗     

LET dependence of lethality of carbon ion irradiation to single tobacco cells

PURPOSE: To determine the radiation sensitivity and relationship between linear energy transfer (LET) and relative biological effectiveness (RBE) in single plant cells irradiated with heavy ions. MATERIALS AND METHODS: Single cells were isolated from the tobacco BY-2 cell line and irradiated with carbon ions (78.6-309 keV microm(-1)) and gamma-rays (0.2 keV microm(-1)). Two weeks after irradiation, colonies with 16 cells or more derived from the irradiated cells were counted as survivors. The surviving fraction was fitted using the single-hit, multitarget theory. RESULTS: The doses needed to reduce the surviving fraction of the cells to 0.1 (D10) of gamma-rays and carbon ions were 47.2 and 10.5-12.6 Gy, respectively. The RBE based on the D10 peaked at an LET of 247 keV microm(-1). The inactivation cross-section of carbon ions reached a plateau of 11.3 microm2 at an LET of 247 keV microm(-1). CONCLUSIONS: The radiation sensitivity of single tobacco cells was much lower than that of mammalian cells, although the mean number of base pairs per chromosome in the two cell types was similar. The RBE peak based on the D10 of carbon ions in single tobacco cells occurred at a higher LET than it does in other organisms.     

The doubling time of regenerating clonogenic cells in the crypts of the irradiated mouse small intestine

The number of clonogenic cells per intestinal crypt has been estimated in control and gamma-irradiated mice, from the response to a single or two test doses. Control unirradiated mice contained 43 +/- 8 clonogenic cells per crypt, which was reduced to about 3 per crypt immediately after 8.0 Gy. After a mitotic delay which was approximately 18 h or 2.25 h/Gy the number of clonogenic cells per crypt increased exponentially with a doubling time of 21 +/- 4 h to reach the control values by about the 4th day postirradiation. The growth curve was related to the changes in total cellularity and the cell production rate per crypt. Since both of these rise during the period of clonogenic regrowth some clonogenic cells must be diverted into the dividing transit cell population, so that the cell cycle time will be shorter than the doubling time given above.